There is a rapidly increasing global demand for metals, particularly rare metals, contained in products such as cell phones and personal computers. However, reserves and production of rare metals are small, and because countries having reserves of these resources are limited, rare metals are subject to rapid price fluctuations, and are politically controlled by countries having these resources. It has thus become very important to keep a stable stock of rare metals. On the other hand, the amounts of wastes of cell phones, personal computers, and other products using rare metals have been increasing sharply, and there is an urgent need for collecting rare metals from these wastes. Such wastes containing rare metals and noble metals are sometimes called urban ores. However, the urban ores are a mixture of a lot of metallic elements, and these metallic elements need to be separately collected. Because the content of each rare metallic element is very small, it has been extremely difficult to selectively collect the desired metallic element with the conventional smelting technique.